Method of sample burning for microchemical combustion analysis



May 1, 1956 P. H. SHERRICK METHOD OF SAMPLE BURNING FOR MICRO-CHEMICAL COMBUSTION ANALYSIS Filed Oct. 2, 1952 3Sheets-Sheet 1 IN V EN TOR. Pa 0/ fiber/7:16

naw 0M May 1, 1956 P. H. SHERRICK 2,743,995

METHOD OF SAMPLE BURNING FOR MICRO-CHEMICAL COMBUSTION ANALYSIS Filed Oct. 2, 2.952 3 Sheets-Sheet 2 JNVENTOR. z je/r/lc BYjM %M May 1, 1956 P. H. SHERRICK METHOD OF SAMPLE BURNING FOR MICRO-CHEMICAL COMBUSTION ANALYSIS Filed Oct. 2, 1952 3 Sheets-Sheet 3 United States Patent METHOD OF SAMPLE BURNING FOR MICRO- CHEMICAL IOMBUSTH'UN ANALYSIS Paul H. Sherrick, Winnetka, Ill., assignor to E.

& Co., a corporation of Illinois H. Sargent This invention relates to a method of sample burning and more particularly to a method of sample burning for micro-chemical combustion analysis of a sample contained in a combustion tube.

In making a micro-chemical combustion analysis it is common laboratory practice to place the sampleto be analyzed in a glass or quartz combustion tube. This tube is generally comprised of four sections, a sample burning section which is the immediate area in the tube about the sample, a preheating section at the entrance end portion of the tube adjacent one end of the sample section, a sweeping section adjacent the other end of the sample section, and a section at the exit end of the tube adjacent the other end of the sweeping section which contains a catalyzing material to insure complete conversion of carbon to carbon dioxide. The tube containing the sample to be analyzed is rapidly heated to a temperature of from 800 C. to 1200 C. or higher, sufiicient to burn the sample. During the period of heating when sample vapors are generated in the tube, oxygen is caused to flow through it downstream from the entrance end through the preheating, sample and sweeping sections respectively and into the heated catalyst section. The sample vapors combine with this oxygen to form gaseous oxides which are carried through the tube by the flow of oxygen and absorbed in absorbing reagents contained in separate vessels which are connected to the exit end of the combustion tube. These vessels are weighed before and after the absorption of the sample vapors.

In making micro-chemical combustion analyses, a number of problems arise, particularly when conducting large volumes of this work. Under such conditions it is necessary to have a standardized heating program technique which etficiently burns the sample, permits substantially all of the generated sample vapors to move into the catalyst section, and gives comparable results. It is therefore important to prevent small losses during sample burning because of the large error produced by such small losses in micro-chemical analysis. To accomplish this, diffusion of the generated sample vapors upstream in the combustion tube toward the preheating section from the sample section should be prevented and in burning the sample condensation or absorption of the generated sample vapors in the preheating section of the combustion tube should be kept at a minimum.

I have discovered a method of sample burning which overcomes these problems. Essentially, the preheating and sample burning Sections of the combustion tube are heated to a predetermined temperature. However, the heating of the sample burning section is initiated after beginning heating of the preheating section and the temperature of the preheating section is maintained at a value greater than that of the sample burning section during generation of any of the sample vapors. A forward moving thermal-gradient is thus set up in the tube during generation of the sample vapors. As a result of this thermal-gradient, the generated sample vapors are prevented from ditfusing upstream toward the preheating section. Instead, they are caused to move downstream toward and into the catalyst section with little or no loss due to back diffusion from the sample section into the preheating section or of condensation in the pre heating and sample sections.

In applying my method, I prefer to employ a tube having a sweeping section located between the catalyst and sample burning section and to heat the catalyst section in order to accelerate oxidation reaction. Under such conditions, the sections are heated to predetermined temperatures. However, heating of the sample section is initiated, after beginning heating of the preheating section; heating of the sweeping section is initiated after beginning heating of the sample section. During the period that sample vapors are being generated and until substantially all of these vapors have moved into the catalyst section, the temperature of the preheating section is maintained at a value greater than that of the sample section, which is maintained at a higher temperature than that of the sweeping section. In this way a forward moving thermal-gradient is set up in the combustion tube moving in the direction of the catalyst section and from the preheating, sample and sweeping sections respectively, until all of the sample vapors have moved into the catalyst section.

In most cases it is desirable to carry out the heating operation rapidly and during heating, causing oxygen to flow through the combustion tube from the entrance end toward the exist end to insure rapid and complete oxidation reaction of the sample vapors.

A radiant type heating furnace suitable for carrying out the process of this invention is illustrated in my copending application, Serial No. 307,681, filed September 3, 1952, now issued as Patent No. 2,671,123 dated March 2, 1954. Details of this apparatus suitable for carrying out the process of this invention are illustrated in the accompanying drawings, in which:

Figure l is a fragmentary, side elevational view of the furnace showing the combustion tube partly in dotted lines;

Figure 2 is an inside end elevational view of the fur nace illustrating the movable half section of the furnace in two positions;

Figure 3 is a fragmentary, side elevational view of the furnace in an open position;

Figure 4 is a fragmentary sectional view taken along line 4-4 of Figure 1;

Figure 5 is a fragmentary sectional view taken along line 55 of Figure 4; and

Figure 6 is a fragmentary, diagrammatic view showing one form of positioning radiant heating furnaces of the type shown in Figures 1-5 so as to practice the method of this invention.

Inasmuch as the structural detail of the furnace is no part of this invention, reference is here made merely to the basic principles thereof.

As illustrated in Figures 1-5, a thin cylindrically shaped casing 10 is comprised of two inter-fitting semicylindrical half sections 11 and 12, preferably made of aluminum. The inner surface of this casing is generally smooth and has an aluminum oxide coating thereon. A self-sustaining resistance wire heating element 13 is positioned within the confines of this casing and adapted to hold a quartz or glass combustion tube 14 therein, concentrically about and parallel to the longitudinal axis of the casing.

The casing 10 includes semicircular shaped end plates 15 which, when the casing is closed, form two opposing circular end plates. Each of these have a hole therethrough to permit the combustion tube 14 to extend beyond the ends of the casing;

As shown in Figures'Z, 3, and 4, one of the half .3 sections "11 of the casing'is'fixedly mounted at the bottom end pottions'atop the support elements "1'6. As here shown, the longitudinally extending edges of this section are about ten degrees from vertical. Theother half section "1'2 'is secured to the end portions of arms '17,

each of'the semi-circular endplatesofithis section being welded to -'one of these arms. The other end (if-each of'these arms is rotatably mounted to upwardly extending posts 18 above the level of thetop of the casing 1'0. By movement of the arms 17 upwardly, ha'lf section"l2 is moved away from fixedly mounted-half section '11, thereby opening the casingll).andpermittinglateral insert'ion and removal of the combustion tube 'l i. his to be noted that opening or the casing lll'in'the above describe'dlma'nner permits rapid .coo'lingo'f a sample-conelements "16 where they are electrically adapted .tobe

connected to an electrical source ofpower .not shownin the drawings. This open-sided heating element 13 is adapted to hold the cornbustiontube 141between the legs of the U-shaped segments -20 and is,positioned within the casing 1% so that the combustion tube, when mounted between the legs of the U shapedsegmentsjis concentric about and extendsparallelf to :the longitudinal axis of the casing 10. In addition, the .open side of the heatingelement 13 faces the .movable half section 12 :in such a manner that a plane passing vthrough the ends of -the uashaped segments 20.is substantially perpendicular to the horizontal ,plane passing .through .the longitudinal axis of the casing 10. .Inthis way, whentheihalf section 124's moved away .from the fixedlymounted half section 11 and to theposition as shown in dottedlines in Figure 2, the combustion tube 14 can be inserted laterally between the legs of the J-shaped segmentslflor removed laterally therefrom.

An example of my new method employing .the .type of furnace described above is ,given below. Aslshown diagrammatically in Figure 6, -the,glass or .quartzcombustiontube 14 may extend throughfour adjacent radiant typeheating furnaces. vided into four adjacent .sections in .the ifollowing sequence: a preheating section :27 at .the :entrance end portion .of the .tube .14, -a sample lburning .sec tion 2'8 adjacent. one end .of the:.preheating-section.27 and which contains a-sample .29 .that is -to "be burned "fonmicrochemical combustion analysis, a sweeping .section 30 adjacent thezother end of thesample section 28, and finally asection 31 adjacent the other end of the preheating section containing catalyzing material32 .to aid in accelerating oxidation of thesample vapors generated during burning of the sample. Eachof the -combustion tube sectionsz27, 28, 30 and Marc enclosedby aseparate stationary furnace23, 24, Hand 26, respectively.

In practicing my method, .the resistance wire. heating element 20a o'fthe furnace .23 :enclosing thepreheating section .27 .is energized throughlitslleadsll'a by anlectrical source not shownin thedrawings to cause heating of this section. Afterenerg izingthe heating elementlfla, theheating element 20b of "furnace 24 enclosingthe burning section ZSis-energized to the point that permits burning of .the sample/29. Following energization of the heating elementlllb, "the heating relement 2000f furnace 25 is then'zenergized. vThe:telectriealgpowerrinput to each of the separate.heating elementstisfcontrolledrso 'a'slto heat the sections .ot' the combustiontube -14 "to;pre-

As here shown, this-tube is diand sweeping sections.

determined temperatures, but during the period in which "sample 'vapors "are generated "from the "sample 29, "the temperature of the preheating section is maintained at a value greater than that of the temperature of the burning sample section, which is maintained at a temperature higher than that of the sweeping section. In this way, a forward moving thermal-gradient is maintained in the combustion tube during generation of any sample vapors and until substantially all of the sample vapors have moved into the catalyst section. Consequently, diffusion of any sample vapors toward the preheating section -tis prevented and-repeated uniform'results can-be obtained whenconducting this work-on a largevolume basis.

While sample vapors are being generated in the combustion tube, the heating element 23d of furnace 26 may be energized and the electrical input to this furnace controlled so that the catalyst material is kept at a selected temperature without change or interruption. In this way the oxidationreaction is accelerated.

During heatingo'f theco'mbustion tub'e'it isprefetredto cause a stream of oxygen to flowthr'oughithe tub'eiin "the direction of and into the catalyst section "31 'lfro'mfthe' preheating section '27 and through the sample "burning As the oxygen'passe's through thetube, 'the"various combustible elements of thes'ample combine with the ox gen to formgaseous oxides. The catalyzin'g'rnaterial through which the gaseous oxidesa're carried insure complete conversion of'carbonto-"cai-bon dioxide "by accelerating the oxidation reaction.

After passing into the catalyst section, the gaseous oxides'=are"caused to how into separate vessels which contain absorbing reagents. These vessels, which are not showninthe'drawings, are weighed before'and after'the absorption an'd'the di'fierence in weight determines the amount 'ofgase'ous oxides absorbed.

In'the above heating procedure, each section of the tube once heated up is held at a temperaturehigher than the next fo'rward section during the time in which the sample burnin'gsection is generating sample burning vapors, and the forward moving'thermal-gradient resulting therefrom is maintained until substantially all of the sample vapors have moved into the catalyst section.

It is to be noted'that in practicing my new methodrof sample'burning, the furnaces employed can be stationary and when operated in the above described manner, a faster operation and shorter over-all time requirement per determination isachieved.

My method of heating the combustion tube .maylbe accomplished by employing any number of separate furnaces or 'by employing a single furnace having :adjacent multiple heating elements within the .casingof-the.

furnace, 'each lementserving to .heat a particular-section and having separate electrical power .input leads .forso heating.

Instead of. having annmber of adjacent multiple heating elements within the casing, the .furnace .may contain a. single .long element with electrical power input utaps topermit sectional-step-wise energizing.

Thef'oregoing detailed description is.-given for clearness of understanding only, and no unnecessary. limitations.

should beunder'stood therefrom, for some modifications will be obviousto those skilled in the art.

:Lclairn:

.1. YThemethod of sample burning.fonmicrowhemieal 'conibustionanalysis of a sample contained in a combustion tube having asarnple burningsectionand a preheating section adjacent one end of the sample section which comprises the steps of: heating the, p'reheating section to a predetermined temperature; thereafter aheating =the samplaheatingsection to a predetermined :temperature lower than thatof the preheatingsection; and-maintaining combustion tube in the direction toward the sample burning section from the preheating section and preventing diffusion of the sample vapors rearwardly toward the preheating section.

2. The method of sample burning for micro-chemical combustion analysis of a sample contained in a combustion tube having a sample burning section, a preheating section adjacent one end of the sample section, and a section containing a catalyst adjacent the other end of the sample burning section which comprises the steps of: heating the preheating section to a predetermined temperature; thereafter heating the sample burning section to a predetermined temperature lower than that of the preheating section; maintaining the temperature of the preheating section higher than that of the sample burning section during generation of any sample vapors in the sample burning section and until substantially all of the sample vapors have moved into the catalyst section thus producing a forward moving thermal-gradient in the combustion tube in the direction toward the catalyst section from the preheating and sample burning sections respectively; heating the catalyst section to a predetermined temperature lower than that of the sample burning section; and maintaining the temperature of the catalyst section lower than that of the sample burning section during generation of any sample vapors in the sample burning section until substantially all of the sample vapors have been moved into the catalyst section.

3. The method as set forth in claim 2 in which oxygen is caused to flow through the combustion tube toward the catalyst section from the preheating and sample burning sections during heating of the sections and until substantially all of the sample vapors move into the catalyst section.

4. The method of sample burning for micro-chemical analysis of a sample contained in a combustion tube having a sample burning section, a preheating section adjacent one end of the burning section, and a sweeper section adjacent the other end of the sample burning section which comprises the steps of: heating the preheating section to a predetermined temperature; thereafter heating the sample burning section to a predetermined temperature lower than the temperature of the preheating section; then heating the sweeping section to a predetermined temperature lower than that of the sample burning section; and maintaining the temperature of the preheating section higher than that of the sample burning section and the temperature of the sample burning section higher than that of the sweeping section during the period that the sample burning section is generating sample vapors thus producing a forward moving thermal-gradient in the combustion tube in the direction toward the sweeping section from the preheating and sample burning section and preventing diffusion of sample vapors rearwardly toward the preheating section.

5. The method or" sample burning for micro-chemical analysis of a sample contained in a combustion tube having a sample burning section, a preheating section adjacent one end of the sample section, a sweeping section adjacent the other end of the sample section, and a section containing a catalyst adjacent the other end of the sweeping section which comprises the steps of: heating the preheating section to a predetermined temperature; thereafter heating the sample burning section to a predetermined temperature lower than the temperature of the preheating section; then heating the sweeping section to a predetermined temperature lower than the temperature of the sample burnin section; maintaining the temperature of the preheating section higher than the temperature of the sample burning section and the temperature of the sample burning section higher than the temperature of the sweeping section during generation of any sample vapors in the sample burning section thus producing a. forward moving thermal-gradient in the combustion tube in the direction toward the catalyst section from the preheating and sample burning sections; heating the catalyst section to a predetermined temperature lower than the temperature of the sweeping section; and maintaining the temperature of the catalyst section lower than the temperature of the sweeping section during generation of any sample vapors in the sample burning section and until substantially all of the sample vapors have moved into the catalyst section. V

6. The method as set forth in claim 5 in which oxygen is caused to flow through the combustion tube toward the catalyst section from the preheating and the sample burning sections during heating of the sections and until substantially all of the sample vapors have moved into the catalyst section.

References Cited in the file of this patent UNITED STATES PATENTS Carr May 6, 1902 Rennie Dec. 13, 1949 OTHER REFERENCES 

5. THE METHOD OF SAMPLE BURNING FOR MICRO-CHEMICAL ANALYSIS OF A SAMPLE CONTAINED IN A COMBUSTION TUBE HAVING A SAMPLE BURNING SECTION, A PREHEATING SECTION ADJACENT ONE END OF THE SAMPLE SECTION, A SWEEPING SECTION ADJACENT THE OTHER END OF THE SAMPLE SECTION, AND A SECTION CONTAINING A CATALYST ADJACENT THE OTHER END OF THE SWEEPING SECTION WHICH COMPRISES THE STEPS OF: HEATING THE PREHEATING SECTION TO A PREDETERMINED TEMPERATURE; THEREAFTER HEATING THE SAMPLE BURNING SECTION TO A PREDETERMINED TEMPERATURE LOWER THAN THE TEMPERATURE OF THE PREHEATING SECTION; THEN HEATING THE SWEEPING SECTION TO A PREDETEMINED TEMPERATURE LOWER THAN THE TEMPERATURE OF THE SAMPLE BURNING SECTION; MAINTAINING THE TEMPERATURE OF THE PREHEATING SECTION HIGHER THAN THE TEMPERATURE OF THE SAMPLE BURNING SECTION AND THE TEMPERATURE OF THE SAMPLE BURNING SECTION HIGHER THAN THE TEMPERATURE OF THE SWEEPING SECTION DURING GENERATION OF ANY SAMPLE VAPORS IN THE SAMPLE BURNING SECTION THUS PRODUCING A FORWARD MOVING THERMAL-GRADIENT IN THE COMBUSTION TUBE IN THE DIRECTION TOWARD THE CATALYST SECTION FROM THE PREHEATING AND SAMPLE BURNING SECTIONS; HEATING THE CATALYST SECTION TO A PREDETERMINED TEMPERATURE LOWER THAN THE TEMPERATURE OF THE SWEEPING SECTION; AND MAINTAINING THE TEMPERATURE OF THE CATALYST SECTION LOWER THAN THE TEMPERATURE OF THE SWEEPING SECTION DURING GENERATION OF ANY SAMPLE VAPORS IN THE SAMPLE BURNING SECTION AND UNTIL SUBSTANTIALLY ALL OF THE SAMPLE VAPORS HAVE MOVED INTO THE CATALYST SECTION. 